Biodegradable polymers are of significant interest due to current environmental concerns. Degradation or break down of the polymer typically occurs by a chemical reaction leading to bond scission in the backbone of a polymer. Degradation ultimately results in reduction in molecular weight. Degradation can occur by chemical, biological, environmental, and/or physical forces. Biodegradable polymers are polymers in which a living organism, such as bacterium, fungus, or enzymes, metabolize or break down the polymer. Known biodegradable polymers include, for example, water-soluble polymers having polyvinylalcohol as base material and polymers containing ester groups in the backbone. Moisture-resistant polymers, such as, hydroxy-butyrate/valerate are produced from natural feedstocks and are also biodegradable. Generally, commercial grade, high molecular weight polyethylenes (PE) are not biodegradable, but low molecular weight (Mw) oligomers (Mw&lt;500) are.
Polyketones, i.e., polymers having carbonyl groups incorporated in the polymer chain, are most commonly produced by polymerizing carbon monoxide with one or more .alpha.-olefins. Peroxidation of the polyketone is one of the methods to prepare selected polyesters, i.e., polymers having oxycarbonyl groups incorporated in the polymer chain. Polyesters are commonly produced by convening keto groups to ester groups. Polyethylene copolymers, such as ethylene/carbon monoxide copolymers (C.sub.2.sup..dbd. /CO), can be converted to polyester copolymers via a Baeyer-Villiger oxidation (ionic, acid-catalyzed) reaction using selected peracids such as peroxyacetic acid (PAA), m-chloroperoxybenzoic acid (MCPBA), trifluoroperoxyacetic acid, peroxymaleic acid, and the like. Such oxidation of C.sub.2.sup..dbd. /CO copolymer was disclosed by Chang et al., U.S. Pat. Nos. 4,929,711 and 4,957,997 and by Austin et al. U.S. Pat. No. 5,180,797. For a general background discussion of conversion of polyketones to polyesters and processes for producing thermoplastic polymer from polyketones, see U.S. '797, '711, and '997, each herein incorporated by reference.
U.S. '711 and '997 to Chang et al. describe batch (as opposed to continuous) reaction processes for converting polyketones to polyesters by reacting a polyketone with an organic peroxyacid oxidizing agent in an inert liquid medium. The ester conversions in these processes typically require over an hour to achieve desirable results. These processes are not practical from a commercial standpoint, because they cannot be readily adapted for mass production of polyesters. Because conversion occurs in a solution phase, the polyester polymer of interest must be precipitated with copious quantities of organic solvents such as methanol. Extended reaction time often results in side reactions such as chain scission or hydrolysis of the ester group and, ultimately, degradation of the molecular weight of the polymer. Generally, the molecular weight of the final polyester product made by the process of U.S. '711 or '997 is not high enough to fabricate articles, fibers, or films.
U.S. '797 to Austin et al., describes conversion of polyketones to polyesters employing a solid or molten reaction phase. Austin et al., specifically disclose a batch process for making a polyester by contacting a solid or molten polyketone with an organic peroxyacid at a temperature from about 20.degree. C. to about 110.degree. C., The process disclosed in U.S. '797 requires the use of solid peracids that are expensive, and the removal of excess reagent, such as excess acid, to purify the polyester polymer desired. Concerns with this procedure include costs and safety, because of the limited choice of solid peracids and the explosive nature of the reagents. Like the process disclosed by Chang et al., the molecular weight of the resulting polyester is typically too low to form products therefrom.
Despite the variety of techniques known for the conversion of keto groups to ester groups, the art lacks a process that allows carbonyl groups incorporated into the polymer chain of a polyketone to be readily oxidized to ester groups in a relatively safe, economical, and commercial scale process which also allows control of molecular weight of the final product. It is desirable to have a commercially feasible, optionally continuous process for the peroxidation of polyketones to polyesters.